Cis-olefins are useful intermediates for the synthesis of many fine chemicals, especially for the synthesis of bioactive materials having a double bond cis-conformed in their structural formula.
In the prior art, cis-olefins were prepared by the hydrogen reduction of alkynes using Lindlar catalysts. Also known in the art are silicon hydride reduction using palladium catalysts (Barley M. Trost, Tetrahedron Letters, Vol. 30, No. 35 pp. 4657, 1989).
These method have several drawbacks. The hydrogen reduction method using Lindlar catalysts is difficult to obtain cis-olefins of high purity since trans-olefins and saturated compounds are by-produced in addition to the desired cis-olefins. The hydrogen reduction method has the danger of a fire. The silicon hydride reduction method must use expensive silicon hydrides and is generally low in cis-olefin selectivity so that trans-olefins can be a major product.
In Tetrahedron, Vol. 44, pp. 481, 1988, A. Arcadi et al discloses formic acid reduction in which aryl iodides are reacted with alkyl 4-hydroxy-2-alkynoates and in the presence of formic acid, tri-n-butylamine and a palladium (II) catalyst.
However, the above formic acid reduction method only provides cyclic product as shown below. No cis-olefins which are pure hydrogenated products are available. ##STR1##
There is a need to have a simple method capable of selectively producing cis-olefins in high yields.